AZEOTROPE-LIKE COMPOSITIONS OF 1,1,1,2,3,3,3-HEPTAFLUOROPROPANE AND 1,1-DIFLUOROETHANE

Abstract: Azeotrope-like compositions of 1,1,1,2,3,3,3-heptafluoropropane and 1,1-difluoroethane useful as aerosol propellants and blowing agents for plastic foams, heat transfer media, fire suppression agents, gaseous dielectrics or blowing agents for plastic foams.

Description: AZEOTROPE-LIKE COMPOSITIONS OF 1,1,1,2,3,3,3-HEPTAFLUOROPROPANE AND 1,1-DIFLUOROETHANE CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of my prior co-pending patent application Serial No. 07/858,240 filed March 26, 1992. BACKGROUND OF THE INVENTION Field of the Invention: The present invention relates to azeotrope-like compositions of 1,1,1,2,3,3,3-heptafluoropropane and 1,1-difluoroethane. These mixtures have no effect on stratospheric ozone and are useful as refrigerants for heating and cooling applications. These mixtures may also be employed as aerosol propellants, heat transfer media, fire suppression agents, gaseous dielectrics or blowing agents for plastic foams. Description of the Prior Art: A number of chlorofluorocarbons (CFCs) have gained widespread use in refrigeration applications owing to their unique combination of physical and chemical properties. However, due to their implication in the destruction of stratospheric ozone, the production and use of CFCs is currently being severely restricted, and the use of these agents will be completely banned in the near future. This will require the replacement of these agents by refrigerants containing neither chlorine nor bromine and which have no effect on stratospheric ozone. One such zero ozone depleting compound which has been proposed is 1,1-difluoroethane, (refrigerant R152a) , which has been shown to provide 4 to 10% increases in efficiency compared to dichlorodifluoromet ane (refrigerant R12), as discussed in Kuijpers, et al., in "CFCs: Time of Transition," ASHRAE, Atlanta, Ga, 1989, p. 175. A major drawback of this compound however is its high flammability. The use of azeotropic mixtures as refrigerants is known in the art, and is discussed for example in R.C. Downing, "Fluorocarbon Refrigerants Handbook," Prentice-Hall, 1988 and R.J. Dossat, "Principles of Refrigeration," 2nd edition, Wiley, 1981. Azeotropic or azeotrope-like compositions do not fractionate upon boiling or evaporation. This behavior is desirable when employing vapor compression equipment for refrigeration, since no fractionation will occur upon evaporation and condensation. Such fractionation can result in undesirable refrigerant distribution and also adversely affect the cooling or heating ability of the system. Non-azeotropic refrigerant mixtures (NARMs) are known in the art, see, e.g., U.S. Patent 4,303,536, but have not found widespread use. Since the NARMs fractionate during the refrigeration cycle, their use may require certain equipment changes. The art is continually seeking new fluorocarbon based azeotrope-like mixtures which offer alternatives for refrigeration and heat pump applications and are efficient, nontoxic, non ozone depleting and nonflammable. As pointed out previously, although efficiency gains are observed employing 1, 1-difluoroethane, its high flammability is a serious liability to its practical use. Computer-based models have substantiated that hydrofluorocarbons such as 1, 1,1,2,3,3,3-heptafluoropropane (HFC227ea) and 1,1-difluoroethane (HFC152a) have no effect on stratospheric ozone, i.e., their ozone depletion potential (ODP) is zero. The use of chloro luorocarbons (CFCs) as blowing agents is well known in the art, but these materials are to be ultimately banned due to their role in the destruction of stratospheric ozone. It is also taught in the art that hydrochlorofluorocarbons (HCFCs), for example 2,2-dichloro-l,1,1-trifluoroethane (CF_CHC1 2 ), are useful in foam blowing applications, see, e.g., I.R. Shankland, Int. J. Refriq.. 13. 113 (1990). However, since the HCFCs are characterized by nonzero ozone depletion potentials, their use will also be restricted and likely banned in the future. it is also well known in the art to employ chlorofluorocarbons (CFCs) as aerosol propellants, see, e.g., R.J. Hodson, in R.E. Banks, ec. , "Organofluorine Chemicals and their Industrial Applications," Horwood, 1979, p. 79. The ultimate ban of these materials due to their role in the destruction of the stratospheric ozone creates, however, a need for environmentally acceptable, nontoxic, nonflammable alternatives. It is accordingly an object of this invention to provide novel azeotrope-like compositions based on 1,1,1,2,3,3,3-heρtafluoropropane and 1,1-difluoroethane wliich are nonflammable, nontoxic, chemically stable, and present no adverse threat to stratospheric ozone. Another object of the invention is to provide novel environmentally acceptable refrigerants which are useful in cooling and heating applications. A further object of the invention is to provide environmentally acceptable, non-toxic, nonflammable aerosol propellants and foam blowing agents. Other objects of the invention will become apparent from the following description. DESCRIPTION OF THE PREFERRED EMBODIMENTS In accordance with the invention, novel azeotrope-like compositions have been discovered comprising 1,1,1,2,3,3,3-heptafluoropropane and 1, 1-difluoroethane. The azeotrope-like compositions comprise from about 55 to about 95 weight percent 1,1, 1,2,3,3,3-heρtafluoropropane and from about 5 to about 45 weight percent 1,1-difluoroethane. These compositions have a boiling point of about -19.0°C at 1 atm. These compositions are azeotrope-like because the composition of said mixtures does not substantially change upon evaporation or condensation. In a preferred embodiment of the invention, such azeotrope-like compositions comprise from about 60 to about 90 weight percent 1,1,1,2,3,3,3-heptafluoropropane and from about 10 to about 40 weight percent 1,1-difluoroethane. The compound 1,1,1,2,3,3,3-heptafluoropropane is known in the art and has been shown to be an efficient fire suppression agent, see, e.g., M. Robin, "Large Scale Testing of Halon Alternatives," 1991 International CFC and Halon Alternatives Conference, Baltimore, MD, December 3-5, 1991. Hence, non-flammable azeotrope-like mixtures are readily obtained by combining 1,1,1,2,3,3,3-heptafluoropropane with 1, 1-difluoroethane. The term "azeotrope-like" is used herein for mixtures of the invention because in the claimed proportions the compositions of 1,1,1,2,3,3,3-heptafluoropropane and 1,1-difluoroethane are constant boiling or essentially constant boiling. Furthermore, no or essentially no fractionation occurs upon evaporating or condensing the mixtures. One method for determining whether a candidate mixture is azeotrope-like is to determine whether the boiling point versus composition curve passes through an extremum, see, e.g., W. Swietoslawski, "Azeotropy and Polyazeotropy, " Pergamon, 1963, and J.M. Smith and H.C. Van Ness, "Introduction to Chemical Engineering Thermodynamics," McGraw-Hill, 1987. Alternatively, one can determine whether a candidate mixture is azeotrope-like by determining whether the vapor pressure versus composition curve passes through an extremum, see, e.g., M. McLinden and G. Morrison, NBS Technical Note 1226, National Bureau of Standards, p. 96, 1986, Smith and Van Ness, op. cit.. and U.S. Patent 4,978,467. Azeotrope-like mixtures which possess a maximum in the vapor pressure versus composition curve will exhibit a minimum in the boiling point versus composition curve. One of the characteristics of an azeotrope-like mixture is that there is a range of compositions containing the same components in varying proportions which are azeotrope-like. It is well known to those skilled in the art that an azeotrope of two compounds represents a unique interaction but with a variable composition depending on the temperature and/or pressure. For example, to those skilled in the art it is understood that the boiling point and composition of an azeotrope will vary with pressure. Accordingly, another way to define an azeotrope-like mixture within the meaning of this invention is to state that such mixtures exhibit vapor pressures within about +/- 5 psia (35 kPa) at 70°F (21°C) of the most preferred compositions disclosed herein (about 65 psia at 70°F (21°C)). As a further alternative, another way to define an azeotrope-like mixture within the meaning of this invention is that given by Bivens (Fluorocarbon Mixtures as CFC Alternatives, 200th ACS National Meeting, Washington, DC, August 18, 1990). As defined by Bivens, "near-azeotropes" are those mixtures for which the dew point/bubble point delta T is less than or equal to 5°C. It is to be understood that the terms "near azeotropes" and "azeotrope-like mixtures" are interchangeable in describing such systems. The mixtures of the present invention are azeotrope-like because for all compositions, the bubble point/dew point delta T is less than 5°C. The inventive compositions are useful in a variety of applications. In one process embodiment of the invention, the azeotrope-like compositions of the invention may be used, in the presence of a suitable lubricant if required, in a method for producing refrigeration which comprises condensing a refrigerant comprising the azeotropic-like compositions and thereafter evaporating the refrigerant in the vicinity of the body to be cooled. In another process embodiment of the invention, the azeotrope-like compositions of the invention may be used, in the presence of a suitable lubricant if required, in a method for producing heating which utilizes condensing a refrigerant comprising the azeotropic-like compositions in the vicinity of the body to be heated, and thereafter evaporating the refrigerant. As will also be readily appreciated by those skilled in the art, the azeotrope-like compositions of the invention are also useful in foam blowing and aerosol propellant applications. It should be understood that the present compositions may include additional, non-interfering components so as to form new azeotrope-like compositions. Any such compositions are considered to be within the scope of the present invention. The present invention is more fully illustrated by the following examples, which are to be understood as exemplary only, and non-limi ing. EXAMPLE 1 This example demonstrates the inertion of HFC-152a by HFC-227ea. The concentration of HFC-227ea required to inert HFC-152a was measured in an 8.0 L explosion sphere, consisting of two 304 stainless hemispheres welded on stainless steel flanges, and equipped with instrumentation allowing the monitoring of pressure and temperature as a function of time. A mixture of HFC-152a and air and the desired concentration of the inerting agent HFC-227ea were introduced into the sphere employing partial pressures to determine the volumes of agent, fuel and air. The mixture was then subjected to a DC spark of 70 J ignition energy, located in the center of the sphere. Mixtures producing an overpressure of greater than or equal to 1.0 psia following activation of the spark are considered flammable, and mixtures producing an overpressure of less than 1.0 psia are considered nonflammable. By examining a series of mixtures of varying ratios of air/fuel/HFC-227ea, the concentration of HFC-227ea required to inert all combinations of the HFC-152a and air can be determined. The flammability measurements indicate that only 8.7% by volume of HFC-227ea is required to render all combinations of HFC-152a and air nonflammable. The flammability diagram determined from the experimental data is shown in FIG. 1 for the HFC-227ea/HFC-152a/air system. A straight line drawn from the origin and not crossing into the flammable region gives the minimum ratio of HFC-227ea to HFC-152a required to provide a nonflammable mixture. It is found that mixtures of HFC-227ea and HFC-152a may contain up to approximately 25 weight percent of HFC-152a and remain nonflammable. EXAMPLE 2 This example demonstrates the azeotrope-like nature of HFC-227ea/HFC-152a mixtures. Vapor pressure data for 80:20 and 30:70 by weight mixtures of HFC-227ea and HFC-152a are shown in Tables 1 and 2. TABLE 1: VAPOR PRESSURE OF A 80:20 BY WEIGHT MIXTURE OF HFC-227ea AND HFC-152a Temperature (F) Pressure (psia) 10.0 1 9 . 7 20.0 24 , . 7 30.0 30 , . 7 40.0 37 , . 6 50.0 46 , . 0 60.0 55 , . 5 70.0 66 , . 0 80.0 78 . . 5 90.0 92 . , 3 100.0 108 . . 0 TABLE 2: VAPOR PRESSURE OF A 30:70 BY WEIGHT MIXTURE OF HFC-227ea and HFC-152a. Temperatvye (F) Pressure (psia) 40.0 43.3 50.0 52.4 60.0 62.7 70.0 74.6 80.0 88.1 90.0 103.5 100.0 121.1 Both sets of data were employed to determine the Carnahan-Starling-DeSantis (CSD) binary interaction coefficient for the mixtures. As described in NBS Technical Note 1226, the CSD binary interaction coefficient allows the calculation of accurate physical and thermodynamic properties for mixtures of fluorinated compounds such as HFC-152a and HFC-227ea. The CSD equation of state accurately describes the physical and thermodynamic properties of fluorocarbons, and their mixtures, and also accurately represents the zeotropic or azeotropic nature of such mixtures. From the vapor pressure data, the binary interaction coefficient was determined following the procedure described by Morrison and McLinden in NBS Technical Note 1226. The binary interaction coefficient was found to be -0.014, and to be independent of the composition of the mixture. The phase (Pxy) diagram for tl»e system HFC-227ea/HFC-152a is shown in FIG. 2; in this figure the upper line is the bubble line (saturated liquid), and the lower line is the dew line (saturated vapor). It is seen from FIG. 2 that the dew point-bubble point delta T is less than 5°C for all compositions. Hence, mixtures of HFC-227ea and HFC-152a are seen to be azeotrope-like over the entire composition range. As an example, an 80:20 by weight mixture of HFC-227ea and HFC-152a is seen from FIG. 2 to be characterized by a bubble point/dew point delta T of 0.7°C. EXAMPLE 3 This example demonstrates the nonflammability of the mixtures. The 80:20 by weight mixture of HFC-227ea and HFC-152a described in Example 2 was tested for flammability in the following fashion. The sample cylinder was placed on a concrete pad and the valve to the cylinder opened slightly to allow the escape of the sample. For a leakage percent from 0 to 100%, the leaking vapor stream could not be ignited with a flame source held approximately 0.5 to 3.0 inches from the location of the leak. A similar test with pure HFC-152a resulted in the ignition of the leaking HFC-152a gas stream to produce a self-propagating flame; the gas stream continued to burn on its own after removal of the flame source. EXAMPLE 4 The foregoing formulations of Examples 1 and 2 are used as propellants, heat transfer media, fire suppression agents, gaseous dielectrics and as blowing agents in conventional fashion, and suitable results are obtained. Having described the invention in detail and by reference to preferred embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims.

Claims: W at is claimed is: 1. An azeotrope-like composition consisting essentially of from about 55 to about 95 weight percent 1,1, 1,2,3,3,3-heptafluoropropane and from about 5 to about 45 weight percent 1, 1-difluoroethane, said composition having a vapor pressure of about 65 psia at 21°C. 2. The composition of claim 1 and which has a vapor pressure of about 65 psia at 21°C. 3. The composition of claim 1 and which consists of the 1,1, 1,2,3,3,3-heptafluoropropane and the 1,1-difluoroethane. 4. The composition of claim 1 and which consists essentially of from about 60 to about 90 weight percent 1,1,1,2,3,3,3-heptafluoropropane and from about 10 to about 40 weight percent 1,1-difluoroethane. 5. The azeotrope-like composition of claim 1 and adapted for use as a refrigerant. 6. The azeotrope-like composition of claim 1 and adapted for use as a propellant. 7. The azeotrope-like composition of claim 1 and adapted for use as a blowing agent. 8. In a method of refrigeration comprising condensing and evaporating an azeotrope-like composition, the improvement comprising using an azeotrope-like composition consisting essentially of from about 55 to about 95 weight percent 1,1,1,2,3,3,3-heptafluoropropane and from about 5 to about 45 weight percent 1,1-difluoroethane. 9. The improvement of claim 8 in which the azeotrope-like composition consists of the 1,1,1,2,3,3,3-heptafluoropropane and the 1, 1-difluoroethane. 10. A method of propelling a composition comprising propelling the composition with an azeotrope-like propellant consisting essentially of from about 55 to about 95 weight percent 1,1,1,2,3,3,3-heptaEluoropropane and from about 5 to about 45 weight percent 1,1-difluoroethane, said composition having a vapor pressure of about 65 psia at 21°C. 11. The method of claim 10 in which the azeotrope-like propellant consists essentially of the 1,1,1,2,3,3,3-heptafluoropropane and the 1, 1-difluoroethane. 12. A method of producing plastic foams from a material which comprises foaming the material with an azeotrope-like composition consisting essentially of from about 55 to about 95 weight percent 1,1,1,2,3,3,3-heptafluoropropane and from about 5 to about 45 weight percent 1,1-difluoroethane, said composition having a vapor pressure of about 65 psia at 21°C. 13. The improvement of claim 12 in which the azeotrope-like composition consists of the 1,1,1,2,3,3,3-heρtafluoropropane and the 1,1-di luoroethane.

Inventors: ROBIN MARK L, ROBIN, MARK, L.
Applicants: GREAT LAKES CHEMICAL CORP, GREAT LAKES CHEMICAL CORPORATION
Application year: 1994
Main classification: C09K3
IPC codes: C07C19, C08J9, C09K3, C09K5